Road markings are typically provided by application of marking materials such as paint, thermoplastic materials, cold hardening materials, preformed lines, and symbols onto the surface of the road. Road marking materials can be applied with or without addition of colors, e.g. white, yellow, or other colors.
Road markings are often profiled to produce a certain surface texture to enhance special properties, e.g. for enhancing retroreflectivity under conditions of wet or rainy weather, or to produce a signal to the driver of a vehicle in the form of an acoustistic signal or vibration when crossed at high speed.
In particular road markings may comprise addition of retro-reflective materials such as glass beads, in particular road markings intended for illumination by vehicle headlamp illumination.
U.S. Pat. No. 4,721,389 discloses a retroreflectivity measuring system that measures performance data relating to a reflective surface, such as a highway stripe or marking containing reflective glass beads. A laser beam illuminates a portion of the reflective surface with radiation of a predetermined wavelength, the laser being incident on the surface at an incidence angle i. The incident laser beam is then reflected back, at least partially, at a particular observation angle o that is separated from the incidence angle by a divergence angle delta. A telephotomultiplier aimed at the illuminated area receives the reflected laser beam at the observation angle o. The laser and the telephotomultiplier may be mounted on a servo-motor driven frame in order to scan the target area from a moving vehicle. Because the intensity of the incident beam is fixed and known, the measured intensity of the reflected laser light in the reflected beam can be used directly for providing a measure of the retroreflectivity of the reflective surface.
Even though the above prior art system provides a measure of the retroreflectivity of a roadmarking, it remains a problem to improve the accuracy of the measurements, in particular when the measurements are performed from a moving vehicle.